Out of interest, whats the difference between the S4 / RS4?

DUDE!
The B5 is well known for pumping out more BHP than quoted.
Unlike the B7 RS4 which is famous for missing it's claimed BHP... often by some distance.

Most B5's are running well over 400bhp since they're so easy to reliably tune.

Pat Y is on the right lines. The differences between the two engines go beyond mere tuning differences and the addition of FSI in the RS4. Below is an excerpt from the 'Audi 4.2 litre V8 FSI Engine self-study programme'. For reference, the 4.2 FSI V8 32v (BNS) engine used in the B7 RS4 is referred to here as 'the high revving engine', whereas the 4.2 V8 40v (BBK) engine used in the B6/7 S4 is referred to as 'the basic engine'. Having owned the latter car for more than two and a half years I'd hardly call its engine 'basic', but everything's relative I suppose.

The main technical differences between the base engine and the high-revving engine lie in the following:

• Crankshaft/connecting rods/pistons
• Timing gear
• Cylinder head
• Oil supply
• Engine cooling
• Intake path
• Exhaust system
• Engine management

The cylinder crankcase of the high-revving engine was machined to higher specifications due to the higher stresses in this component. To minimize warping of the cylinder manifolds, the crankcase is honed under stress. For this purpose, a honing template is attached to the crankcase before the honing process in order to simulate the warping of the bolted-on cylinder manifold.

Modifications to High-revving Engine:
At very high engine speeds, axial vibration occurs due to the unbalance in the single-mass damper. This can cause the crankshaft to break.

To avoid this vibration, a dual-mass damper without unbalance is employed in the high-revving engine. To compensate for unwanted engine vibration, heavy metal inserts are integrated in the first and eighth crank journals by way of unbalance.

Connecting Rod:
Cracked connecting rods made of 36MnVS4 are used in the basic engine, while the conventionally split connecting rods in the RS4 engine are made of 34CrNiMo8, for strength.

In addition, the geometry and tolerances of the
connecting rods were reduced on the high revving version of the 4.2L V8 FSI engine.

Bearing journals diameter: 54 mm
Bearing bushings: 1.4 mm thick, 15.25 mm wide
Length of bushing: 0.20 mm diameter rolled
Connecting rod length: 154 mm

Piston:
For strength reasons, forged pistons with a slightly higher weight than conventional pistons, are used. Both engines have the same piston geometry.
Piston weight without rings: approximately 290 g (10 oz)
Piston pin: 0.20 mm x 0.11.5 mm x 40 mm

High-revving Engine:

• 3/8" simplex sleeve-type chains are used here. Their advantage is their reduced wear and higher stress resistance at high engine speeds. In this case the idler gears have 38 and 19 teeth. The camshaft sprockets have 25 teeth.

Different Features of the High-revving Engine:

• To match the higher engine power output and RPM, the following cylinder head components were modified:
• Intake ports are charge optimized (based on larger cross-sections)
• Intake valves are chrome-plated hollow stem valves (for weight reduction)
• Valve springs are made of a material with higher tensile strength and also have higher spring force
• To meet the higher fuel requirements, the injectors are designed for higher flow rates.
• Roller rocker arms are more robustly designed, with peened rollers for higher strength
• Camshafts have different timings and larger opening lengths
• Intake valve opening angle 230 crank angle degrees
• Exhaust valve opening angle 220 crank angle degrees
• The lifters were adapted from the 3.2L V6 engine found in the TT and A3. They have a larger ball stroke which, in the course of testing, proved advantageous for the high-revving engine (with regard to the inflation of the hydraulic valve clearance compensation element).
• The cylinder head has a modified water jacket which circulates coolant to the area between the intake port and the injector, thereby reducing the temperatures in the cylinder head combustion chamber plate.
• Due to a modified camshaft drive reduction ratio, the camshaft adjuster has 25 teeth for the chain drive, as opposed to 30 teeth in the basic engine.

In the more highly stressed high-revving engine, an additional oil-air heat exchanger is used to minimize the oil temperature even at high engine load. This additional heat exchanger is operated in parallel with the heat exchanger via a thermostat.

Audi RS4 Sump:
A reliable supply of oil in all driving situations is critical, especially in a sports car such as the RS4. The oil supply system in the high-revving engine was designed for racing applications in which it is subjected to
lateral acceleration of up to 1.4 g. To ensure this, the sump in the RS4 has an additional system of flaps.

Design:
Four flaps, whose axis of rotation is parallel to the longitudinal axis of vehicle, are arranged inside a housing. Each of the flaps opens toward the inside of the intake end of the oil pump.

Function:
When the vehicle is cornering, the oil flows inside the sump toward the outside of the corner. The two flaps facing the outside of the corner close and hold the oil in the sump intake. At the same time, the two flaps facing the inside of the corner open to allow additional oil to flow into the intake. This ensures a sufficient supply of oil to the oil pump.

The intake system of the RS4 engine was designed with emphasis on maximum flow control. Pressure loss is minimized by a large cross-sectional areas in the Mass Air Flow (MAF) Sensor G70 and air intake pipe in combination with a 90 mm diameter throttle valve.

To ensure a sufficient supply of air to the engine at high RPM, the power flap in the air filter is opened at engine speeds higher than 5000 RPM and at road speeds higher than 200 kph.
The power flap is opened and closed by a vacuum actuator which is map-controlled by the ECM via the Intake Air Switch-Over Valve N335.

The sand cast aluminum (should be magnesium) intake manifold was designed specifically to match the sporty characteristic of the engine. In contrast to the basic engine, maximum torque is produced at higher engine RPM. At this engine speed, the intake manifold changeover valve would be switched to the short path for higher power output.

Spark Plugs:
In contrast to the Audi Q7, spark plugs with a higher heatrating (colder plugs)* are used because the RS4 engine is subjected to higher thermal stresses.

• applies to NGK spark plugs

Injectors:
Due to the higher fuel demand and the shorter window of time available for injection at very high engine speeds, the RS4 engine is fitted with larger injectors than the Audi Q7 engine.

Other differences include the incorporation of Audi's DRC (Dynamic Ride Control) sports suspension mechanism on the B7 RS4. With DRC, a fluid mechanical linkage between diagonally opposing front and rear suspension dampers is used to counteract vehicle pitch and roll.

The Torsen quattro setup on the B6/7 S4 is split 50/50 between front and rear axles; the B7 RS4 is 40/60.

B6/7 S4 brakes consisted of radially vented discs front and rear, the fronts sized at 345mm x 30mm thick, and rears at 302mm x 20mm. Single-piston sliding brake calipers front and rear clamp the discs. Standard brakes on the B7 RS4 consist of cross-drilled, radially ventilated and floating 365mm iron front brake discs with Brembo eight-piston calipers. Rear brakes are drilled, vented and floating 320mm x 22mm iron discs with single piston floating caliper.

B6/7 standard alloy wheels were 'AVUS-III' die-cast aluminium alloy, 8Jx18" ET45 in size, and shod with 235/40 ZR18 95Y XL high performance tyres. B7 RS4 standard wheels are 9Jx19" ET29 '7-arm double spoke' alloys with 255/35 ZR19 96Y XL high performance tyres. A no-cost option of 18" alloy wheels (8½Jx18" '5-spoke design') with 255/40 ZR18 95Y XL tyres was also available.

The B7 RS4 also has lightweight aluminium wings and bonnet, whereas the S4 uses conventional steel.

Unfortunately, they were among the worst of the Audis in terms of how they felt to drive. The B7 is a world apart from recent offerings, and really should not be compared to earlier RS4s.

The current RS6 is the spiritual successor to the last RS4; the Rs2 is a better bet for the progenitor of the B7 RS4.